This invention relates to a fire barrier composition, to a method of using the fire barrier composition in which a flammable substrate is coated with the composition to protect the substrate from fire, and to a method for encapsulating lead paint using the composition of this invention.
Numerous methods have been developed for protecting objects from fire. The rationale for each of these methods is found in the physics of combustion, the chemistry of flame, and the engineering of fire control systems. Many of these methods involve the use of fire protective coatings forming a barrier system intended to prevent the ignition and spread of flame on a combustible substrate.
Four types of fire protective coatings are known: (1) ablative; (2) intumescent; (3) sublimation and gas- or vapor-producing; and (4) "ceramic" or inorganic. Ablative coatings are generally thick, heavy, and costly, thus limiting their application to special uses. Intumescent coatings are generally soft and easily abraded and have a limited duration of protection--10 to 15 minutes when exposed to fire. Sublimative or gas-producing coatings have an even shorter duration of protection--after the fire retardant gases have been produced and wafted away from the surface, the flammable substrate is left without a protective mechanism. Such coatings have found their major use in the treatment of fibers and clothing. Ceramic coatings, as the name implies, require high temperature curing in order to form a ceramic bond. Unfortunately, many structural or building components cannot withstand this treatment. Inorganic coatings, such as Portland cement, gypsum, calcium aluminate cement, phosphate-bonded cement, metal-pigment loaded silicate coatings, high-temperature silicone, and magnesium "oxysalt" cements, have also been proposed.
A commonly used fireproofing coating is derived from a magnesium oxychloride cement. This cement is made by mixing magnesium chloride and magnesium oxide with other materials to form a viscous, cementitious mixture that can be applied to the surface of the object to be fireproofed. Unfortunately, some magnesium oxychloride coatings, as well as fireproofing coatings derived from other oxysalt cements, have significant shortcomings. For example, these cements tend to be brittle, rigid, and susceptible to spalling or decrepitating under heat. The coatings also exhibit poor aging and weatherability characteristics. In addition, there is a loss of tensile strength and cohesiveness after exposure to flame.
Thus, an ideal flame-retardant coating should be quick-setting, non-combustible, and capable of protecting a variety of susceptible flammable substrates from ignition, while overcoming the above-listed shortcomings observed previously. It has recently been found that a magnesium oxychloride cement cobonded with a high alumina calcium aluminate cement and a colloidal silica fulfills some of these needs in the art. Such a composition, in the form of a thin paint, does not spall, decrepitate or crack significantly under direct flame impingement and exhibits an adequate tensile and cohesive strength for the duration of a fire. In addition, this cement has all of the properties of a good paint exhibiting excellent adhesion properties to a wide range of substrates.
While this fireproofing cement represents a major step forward in meeting many of the needs in the art, there exists a need to modify the properties of the composition to suit certain applications. The pot-life of the cement is inconveniently short for some industrial and commercial applications; after mixing the components together, the viscosity of the mixture increases rapidly, rendering it unworkable after 15 to 20 minutes. Additionally, some decrepitation has been noted when a flame is rapidly and directly impinged on the coating.
As the batch-size of a composition is limited to the quantity that can be applied to a substrate during its pot-life, a longer pot-life increases the efficiency with which the coating can be applied. Therefore, there exists a need in the art for a magnesium oxysalt flame retardant coating that exhibits a significantly longer pot-life. Ideally, the coating should also be more resistant to decrepitation upon direct flame impingement.
In addition to the flame retardant properties of a magnesium oxysalt coating, there exists other divergent needs in the art that such a coating could aid in fulfilling. For example, it is well known that lead-based paints present serious health dangers to small children. Consequently, there is a need to encapsulate such paints. The encapsulating agent should be a virtually impenetrable barrier that is not compromised even under the harshest conditions.